This invention relates to cameras, and in particular to an apparatus for determining when the supply of film in a camera has been exhausted. The invention will be described herein as utilized in a security camera with the film carried in a cartridge or cassette, but it will be realized that the invention is not limited to this specific end use or film source.
A typical security camera includes a supply of film loaded in a cartridge for easy insertion into and removal from the camera, with the film being advanced by a motor incorporated in the camera. The camera is mounted in a remote location and the motor which both advances the film and actuates the shutter is controlled by an electrical circuit including an alarm switch. The alarm switch may be manually actuated by personnel or may be actuated by intrusion detection devices.
When the film supply in the camera is exhausted, the exposed film needs to be removed and a fresh supply of film installed. It is highly desirable to have an automatic arrangement for indicating when the film supply is exhausted, and for shutting off the power to the motor to stop camera action. A variety of devices for detecting the presence or absence of film, tapes or other strips have been developed. Many of the present devices utilize a light source and a light detector with the light path being directed through sprocket holes or other holes in the film edge. Typical configurations are shown in U.S. Pat. Nos. 4,401,376 to Pomazi and 4,174,888 to Hunn et al. An alternative arrangement utilizes specially coded sections along the film strip, as shown in U.S. Pat. No. 3,967,887 to Suzaki et al.
U.S. Pat. No. 4,373,796 to Matusura et al. utilizes a light source and a light detector positioned on opposite sides of a rotating disk, which disk is driven by the motor which drives the film. While this device provides for shutting off power to the motor when the film supply is used up, it is actually detecting film motor drive action rather than the presence or absence of film.
U.S. Pat. No. 4,391,812 to Williams shows a system with a variety of codes for reading film for projection, including a reflective cue inserted into the margin of the film.
Many of these prior art concepts require special treatment of the film prior to its use. Other of the prior art concepts require access to both sides of the film during use. Hence these prior art configurations are not suitable for use with conventional film cartridges. It is an object of the present invention to provide a new and improved end of film detection device which is readily incorporated into standard camera designs and which can be used with standard film cartridge designs. Other objects, advantages, features and results will more fully appear in the course of the following description.